David Valleau's recipe comes from the chef's experiences working in small fish restaurants in Southern California. It's an adaptation of what cooks from Guadalajara made for themselves in the kitchen, says David. Lime juice, cilantro, and pepper, he adds, is the holy trinity-acid, spice, and herb-of Mexican fish tacos. When it comes to purchasing and handling cod, David suggests adhering to the seafood importers' motto: quick, cold, and clean. What's most important, he says, is how fresh it is, how quickly it gets to market.